Many probes used for ultrasound imaging, particularly those probes with a 2D matrix array, such as those currently used for 3D/4D imaging, have arrays with a large number of discrete transducer elements. For example, many conventional probes using a 2D matrix array have more than 1,000 transducer elements. There are significant design constraints associated with the probe cable used to transmit signals from the elements to a beamformer on the system-side for the generation and display of images based on the ultrasound data.
Conventional probe cables require a separate lead or wire to transmit the signal associated with each unique channel. For example, if the ultrasound system has 256 channels, the probe cable will require 256 separate leads. It is not practical or economical to have an individual lead for each element for a contemporary probe with a 2D matrix array, which may have several thousand elements. Adding additional leads to a probe cable significantly increases the cost of the probe cable, and it results in a thicker, heavier, bulkier, less flexible probe cable. It is desirable to keep the probe cable relatively light, thin, and flexible in order to make scanning as ergonomic as possible for clinicians.
Due to the increasing number of transducer elements in contemporary probes and due to the aforementioned desired characteristics for probe cables, there is a significant incentive to perform an analog-to-digital conversion and at least some partial beamforming within the probe in order to reduce the number of channels required to transfer the signals from the probe to the system-side of the ultrasound imaging system.
It is desirable to use an analog-to-digital converter with a relatively broad dynamic range and a high temporal resolution. In order to make the probe ergonomic, it is desirable to minimize the overall size of the probe. Additionally, power use and resulting heat generation are always of concern for probes. As such, it is desirable to use a component for the analog-to-digital conversion that is relatively compact and efficient from a power consumption perspective. A delta-sigma modulator is an analog-to-digital converter that meets the above-stated needs very well.
However, a delta-sigma modulator requires sampling that is uniform in time. This condition is not met during delay-expansion periods, such as when performing dynamic receive focusing. The use of conventional techniques with delta-sigma modulators results in unwanted noise due to some samples being repeated multiple times during delay expansion periods. The high levels of noise due to non-uniform sampling in time have made it difficult or impossible to leverage the high sampling frequency and low power consumption of delta-sigma modulators for analog-to-digital conversion within probes used for ultrasound imaging. Therefore, a delta-sigma beamformer, an ultrasound imaging system, and a method for beamforming using delta-sigma modulators is desired for at least the reasons discussed hereinabove.